Automated fiber placement is a technique of manufacturing fiber-reinforced composite components. The technique uses automated fiber placement (AFP) machines (also called advanced fiber placement machines) that precisely place and layer strips of uncured fiber tape onto molds and/or mandrels, AFP machines typically are used to fabricate large-scale, complex-shaped structures such as airframes, air turbine blades, pressure vessels, and other industrial products.
The uncured fiber tape commonly includes carbon fibers pre-impregnated with thermoset and/or thermoplastic materials (a prepreg carbon fiber tape). The tape may be in the form of a tow, which is an untwisted bundle of continuous filaments, and may be thin and narrow (common thicknesses range from about 0.005″ (0.13 mm) to 0.010″ (0.25 mm); common widths range from about 0.125″ (3 mm) to about 0.5″ (13 mm)).
AFP machines typically have a capacity to place a plurality (e.g., 2-32) of strips of tape together in parallel and thus may form a single band with a width as wide as the sum of the widths of the strips. AFP machines may place the strips in a range of orientations (e.g., 0°, +45°, −45°, and/or 90°) across a range of layup mold and/or mandrel shapes (e.g., flat, concave, and/or convex). Machines limited to essentially flat or basic contours may be referred to as automated tape laying machines, automated flat tape laying machines, and/or automated contour tape laying machines.
AFP machines typically include automated cutting of the tape into strips and layering of the strips to form plies (each a single strip layer). Further, AFP machines may compact new strip layers onto the underlying plies. The layers of a composite part need to properly contact and adhere to each other for proper lamination and cure. Where new strip layers fail to adhere to the underlying layers (with or without AFP machine compacting), inter-laminal voids form in the uncured and cured part. Inter-laminal voids are a delamination defect that may lead to weakness in the cured composite part. Hence, there is a need to detect and repair inter-laminal voids, preferably before curing a composite part.